draft-ietf-dhc-client-id-07.txt   rfc6842.txt 
DHC Working Group N. Swamy Internet Engineering Task Force (IETF) N. Swamy
Internet-Draft Samsung India Request for Comments: 6842 Samsung India
Updates: 2131 (if approved) G. Halwasia Updates: 2131 G. Halwasia
Intended status: Standards Track P. Jhingran Category: Standards Track P. Jhingran
Expires: May 9, 2013 Cisco Systems ISSN: 2070-1721 Cisco Systems
November 5, 2012 January 2013
Client Identifier Option in DHCP Server Replies Client Identifier Option in DHCP Server Replies
draft-ietf-dhc-client-id-07
Abstract Abstract
This document updates RFC 2131 -- Dynamic Host Configuration Protocol This document updates RFC 2131 "Dynamic Host Configuration Protocol"
(DHCP) -- by addressing the issues arising from that document's by addressing the issues arising from that document's specification
specification that the server MUST NOT return the 'client identifier' that the server MUST NOT return the 'client identifier' option to the
option to the client. client.
Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on May 9, 2013. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6842.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................2
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language ......................................2
3. Modification To [RFC2131] . . . . . . . . . . . . . . . . . . . 4 2. Problem Statement ...............................................2
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 3. Modification to RFC 2131 ........................................3
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 4. Security Considerations .........................................4
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgments .................................................4
7. Normative References . . . . . . . . . . . . . . . . . . . . . 5 6. Normative References ............................................4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
The Dynamic Host Configuration Protocol (DHCP) defined in [RFC2131] The Dynamic Host Configuration Protocol (DHCP) defined in [RFC2131]
provides configuration parameters to hosts on an IP based network. provides configuration parameters to hosts on an IP-based network.
DHCP is built on a client-server model, where designated DHCP servers DHCP is built on a client-server model, where designated DHCP servers
allocate network addresses and deliver configuration parameters to allocate network addresses and deliver configuration parameters to
dynamically configured hosts. dynamically configured hosts.
The changes to [RFC2131] defined in this document clarify the use of The changes to [RFC2131] defined in this document clarify the use of
the 'client identifier' option by the DHCP servers. The the 'client identifier' option by the DHCP servers. The
clarification addresses the issues (as mentioned in Problem clarification addresses the issues (as mentioned in Problem
Statement) arising out of the point specified by [RFC2131] that the Statement) arising out of the point specified by [RFC2131] that the
server 'MUST NOT' return 'client identifier' option to the client. server MUST NOT return the 'client identifier' option to the client.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Problem Statement 2. Problem Statement
[RFC2131] specifies that a combination of 'client identifier' or [RFC2131] specifies that a combination of 'client identifier' or
'chaddr' and assigned network address constitute a unique identifier 'chaddr' and assigned network address constitute a unique identifier
for the client's lease and are used by both the client and server to for the client's lease and are used by both the client and server to
identify a lease referred in any DHCP messages. [RFC2131] also identify a lease referred in any DHCP messages. [RFC2131] also
specifies that the server "MUST NOT" return 'client identifier' in specifies that the server MUST NOT return the 'client identifier'
DHCPOFFER and DHCPACK messages. Furthermore, DHCP relay agents and option in DHCPOFFER and DHCPACK messages. Furthermore, DHCP relay
servers implementing [RFC2131] "MAY" drop the DHCP packets in the agents and servers implementing [RFC2131] MAY drop the DHCP packets
absence of both 'client identifier' and 'chaddr'. in the absence of both the 'client identifier' and 'chaddr' option.
In some cases, a client may not have a valid hardware address to In some cases, a client may not have a valid hardware address to
populate the 'chaddr' field and may set the field to all zeroes. One populate the 'chaddr' field and may set the field to all zeroes. One
such example is when DHCP is used to assign IP address to a mobile such example is when DHCP is used to assign an IP address to a mobile
phone or a tablet and where the 'chaddr' field is set to zero in DHCP phone or a tablet and where the 'chaddr' field is set to zero in DHCP
request packets. In such cases, client usually sets the 'client request packets. In such cases, the client usually sets the 'client
identifier' option field (to a value as permitted in [RFC2131]), and identifier' option field (to a value as permitted in [RFC2131]), and
both client and server use this field to uniquely identify the client both the client and server use this field to uniquely identify the
with in a subnet. client with in a subnet.
Note that due to above mentioned recommendations in [RFC2131], valid Note that due to aforementioned recommendations in [RFC2131], valid
downstream DHCP packets (DHCPOFFER, DHCPACK and DHCPNAK) from the downstream DHCP packets (DHCPOFFER, DHCPACK, and DHCPNAK) from the
server MAY get dropped at the DHCP relay agent in the absence of server MAY get dropped at the DHCP relay agent in the absence of the
'client identifier' option when 'chaddr' field is set as zero. 'client identifier' option when the 'chaddr' field is set to zero.
The problem may get aggravated when a client receives a response from The problem may get aggravated when a client receives a response from
the server without 'client identifier' and with 'chaddr' value set to the server without 'client identifier' and with the 'chaddr' value
zero, as it cannot guarantee that the response is intended for it. set to zero, as it cannot guarantee that the response is intended for
This is because even though the 'xid' field is present to map it. This is due to the fact that even though the 'xid' field is
responses with requests, this field alone cannot guarantee that a present to map responses with requests, this field alone cannot
particular response is for a particular client, as 'xid' values guarantee that a particular response is for a particular client, as
generated by multiple clients within a subnet need not be unique. 'xid' values generated by multiple clients within a subnet need not
be unique.
Lack of 'client identifier' option in DHCP reply messages also Lack of the 'client identifier' option in DHCP reply messages also
affects the scenario where multiple DHCP clients may be running on affects the scenario where multiple DHCP clients may be running on
the same host sharing the same 'chaddr'. the same host sharing the same 'chaddr'.
This document attempts to address these problems faced by DHCP relay This document attempts to address these problems faced by the DHCP
agent and client by proposing modification to DHCP server behavior. relay agent and client by proposing modification to DHCP server
The solution specified in this document is in line with DHCPv6 behavior. The solution specified in this document is in line with
[RFC3315] where the server always includes the Client Identifier DHCPv6 [RFC3315] where the server always includes the Client
option in the Reply messages. Identifier option in the Reply messages.
The requirement for DHCP servers not to return the 'client The requirement for DHCP servers not to return the 'client
identifier' option was made purely to conserve the limited space in identifier' option was made purely to conserve the limited space in
the packet. It is possible, though unlikely, that clients will drop the packet. It is possible, though unlikely, that clients will drop
packets that contain this formerly unexpected option. There are no packets that contain this formerly unexpected option. There are no
known client implementations that will drop packets but the benefit known client implementations that will drop packets, but the benefit
provided by this change outweighs any small risk of such behavior. provided by this change outweighs any small risk of such behavior.
More harm is being done by not having the 'client identifier' option More harm is being done by not having the 'client identifier' option
present than might be done by adding it now. present than might be done by adding it now.
3. Modification To [RFC2131] 3. Modification to RFC 2131
If the 'client identifier' option is present in a message received If the 'client identifier' option is present in a message received
from a client, the server MUST return the 'client identifier' option, from a client, the server MUST return the 'client identifier' option,
unaltered, in its response message. unaltered, in its response message.
Following table is extracted from section 4.3.1 of [RFC2131] and The following table is extracted from Section 4.3.1 of [RFC2131] and
relevant fields are modified accordingly to overcome the problems relevant fields are modified accordingly to overcome the problems
mentioned in this document. mentioned in this document.
Option DHCPOFFER DHCPACK DHCPNAK Option DHCPOFFER DHCPACK DHCPNAK
------ --------- ------- ------- ------ --------- ------- -------
Client identifier (if MUST MUST MUST Client identifier (if MUST MUST MUST
sent by client) sent by client)
Client identifier (if MUST NOT MUST NOT MUST NOT Client identifier (if MUST NOT MUST NOT MUST NOT
not sent by client) not sent by client)
When a client receives a DHCP message containing a 'client When a client receives a DHCP message containing a 'client
identifier' option, the client MUST compare that client identifier to identifier' option, the client MUST compare that client identifier to
the one it is configured to send. If the two client identifiers do the one it is configured to send. If the two client identifiers do
not match, the client MUST silently discard the message. not match, the client MUST silently discard the message.
4. IANA Considerations 4. Security Considerations
This memo asks the IANA for no new parameters.
5. Security Considerations
This specification does not add any new security considerations other This specification does not add any new security considerations other
than the ones already mentioned in [RFC2131]. It is worth noting than the ones already mentioned in [RFC2131]. It is worth noting
that DHCP clients routinely connect to different IP networks managed that DHCP clients routinely connect to different IP networks managed
by different network providers. DHCP clients have no a priori by different network providers. DHCP clients have no a priori
knowledge of which network they are connecting to. Consequently, the knowledge of which network they are connecting to. Consequently, the
client identifier will, by definition, be routinely shared with client identifier will, by definition, be routinely shared with
network operators and could be used in ways that violate the user's network operators and could be used in ways that violate the user's
privacy. This is a problem that existed in [RFC2131]. This document privacy. This is a problem that existed in [RFC2131]. This document
does nothing to address this problem. does nothing to address this problem.
6. Acknowledgments 5. Acknowledgments
The authors would like to thank Bernie Volz, Ted Lemon, Barr Hibbs, The authors would like to thank Bernie Volz, Ted Lemon, Barr Hibbs,
Richard Johnson, Barry Leiba, Stephen Farrell, Adrian Farrel for Richard Johnson, Barry Leiba, Stephen Farrell, and Adrian Farrel for
insightful discussions and review. insightful discussions and review.
7. Normative References 6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", [RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997. RFC 2131, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003. IPv6 (DHCPv6)", RFC 3315, July 2003.
Authors' Addresses Authors' Addresses
Narasimha Swamy Nelakuditi Narasimha Swamy Nelakuditi
Samsung India Samsung India
Block-B, Bagmane Lakeview, Block-B, Bagmane Lakeview,
66/1, Bagmane Tech Park, 66/1, Bagmane Tech Park,
Byrasandra, C.V. Raman Nagar, Bangalore, 560093 Byrasandra, C.V. Raman Nagar, Bangalore, 560093
India India
Phone: +91 80 4181 9999 Phone: +91 80 4181 9999
Email: nn.swamy@samsung.com EMail: nn.swamy@samsung.com
Gaurav Halwasia Gaurav Halwasia
Cisco Systems Cisco Systems
SEZ Unit, Cessna Business Park SEZ Unit, Cessna Business Park
Sarjapur Marathalli Outer Ring Road Sarjapur Marathalli Outer Ring Road
Bangalore, 560103 Bangalore, 560103
India India
Phone: +91 80 4426 1321 Phone: +91 80 4426 1321
Email: ghalwasi@cisco.com EMail: ghalwasi@cisco.com
Prashant Jhingran Prashant Jhingran
Cisco Systems Cisco Systems
SEZ Unit, Cessna Business Park SEZ Unit, Cessna Business Park
Sarjapur Marathalli Outer Ring Road Sarjapur Marathalli Outer Ring Road
Bangalore, 560103 Bangalore, 560103
India India
Phone: +91 80 4426 1800 Phone: +91 80 4426 1800
Email: pjhingra@cisco.com EMail: pjhingra@cisco.com
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